Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital audio broadcasting (DAB), uses terrestrial transmitters in the existing Medium Frequency (MF) and Very High Frequency (VHF) radio bands. HD Radio™ technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception. IBOC DAB signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers or in an all-digital format wherein the analog modulated carrier is not used. Using the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog-to-digital radio while maintaining their current frequency allocations.
One feature of digital transmission systems is the inherent ability to simultaneously transmit both digitized audio and data. Thus the technology also allows for wireless data services from AM and FM radio stations. The broadcast signals can include metadata, such as the artist, song title, or station call letters. Special messages about events, traffic, and weather can also be included. For example, traffic information, weather forecasts, news, and sports scores can all be scrolled across a radio receiver's display while the user listens to a radio station.
IBOC DAB technology can provide digital quality audio, superior to existing analog broadcasting formats. Because each IBOC DAB signal is transmitted within the spectral mask of an existing AM or FM channel allocation, it requires no new spectral allocations. IBOC DAB promotes economy of spectrum while enabling broadcasters to supply digital quality audio to the present base of listeners.
Multicasting, the ability to deliver several programs or data streams over one channel in the AM or FM spectrum, enables stations to broadcast multiple streams of data on separate supplemental or sub-channels of the main frequency. For example, multiple streams of data can include alternative music formats, local traffic, weather, news, and sports. The supplemental channels can be accessed in the same manner as the traditional station frequency using tuning or seeking functions. For example, if the analog modulated signal is centered at 94.1 MHz, the same broadcast in IBOC DAB can include supplemental channels 94.1-1, 94.1-2, and 94.1-3. Highly specialized programming on supplemental channels can be delivered to tightly targeted audiences, creating more opportunities for advertisers to integrate their brand with program content. As used herein, multicasting includes the transmission of one or more programs in a single digital radio broadcasting channel or on a single digital radio broadcasting signal. Multicast content can include a main program service (MPS), supplemental program services (SPS), program service data (PSD), and/or other broadcast data.
The National Radio Systems Committee, a standard-setting organization sponsored by the National Association of Broadcasters and the Consumer Electronics Association, adopted an IBOC standard, designated NRSC-5A, in September 2005. NRSC-5A, the disclosure of which is incorporated herein by reference, sets forth the requirements for broadcasting digital audio and ancillary data over AM and FM broadcast channels. The standard and its reference documents contain detailed explanations of the RF/transmission subsystem and the transport and service multiplex subsystems. Copies of the standard can be obtained from the NRSC at http://www.nrscstandards.org/standards.asp. iBiquity's HD Radio™ technology is an implementation of the NRSC-5A IBOC standard. Further information regarding HD Radio™ technology can be found at www.hdradio.com and www.ibiguity.com.
Other types of digital radio broadcasting systems include satellite systems such as XM Radio, Sirius and WorldSpace, and terrestrial systems such as Digital Radio Mondiale (DRM), Eureka 147 (branded as DAB), DAB Version 2, and FMeXtra. As used herein, the phrase “digital radio broadcasting” encompasses digital audio broadcasting including in-band on-channel broadcasting, as well as other digital terrestrial broadcasting and satellite broadcasting.
It would be desirable to have a portable or hand-held FM digital radio receiver device. However, existing FM analog portable and hand-held radio receiver devices typically have very poor reception. These devices present several challenges, including small size and weight, EMI caused by antenna proximity to electronics, variability due to the effects of the human body, and the need to support indoor reception. Currently, portable and hand-held analog radio receivers may use an earbud-wire type antenna, which may be either a dipole or monopole. An earbud dipole antenna solution yields poor performance due to the limited distance between the ears for the upper and lower elements of the antenna, whereas a monopole earbud antenna solution requires the addition of a ground plane to replace the lower-half element of a dipole. Ideally, the ground plane is approximately a quarter wavelength in size. However, today's hand-held devices are typically much smaller. One way to improve a ground plane is to include a meander (spiral) loop. Such a loop increases the effective ground plane size and the inductance of the spiral reduces high capacitive reactance. The meander-loop type antenna is presently found in cell phones and in some table-top radio receivers, but not in portable radio devices. A better approach would be to use antenna elements that do not require a ground plane. The quality of reception for both monopole and dipole earbud antennas is variable and unpredictable, depending significantly on the orientation of the user and the antenna elements. Movement or touching of the antenna or receiver by the user can change the quality of the signal, which the human body itself can attenuate. Moreover, EMI between the antenna and nearby electronic elements such as the power supply can contribute to loss in performance. In addition, these antennas have unbalanced impedance. The impedance is orientation-dependant and impedance matching to the receiver is lossy. To overcome these problems, one existing solution is to include the antenna in a docking station for the hand-held receiver. This solution is undesirable, however, because the antenna element is not portable and cannot travel with the user. It would be desirable to have an antenna design that overcomes these and other problems, particularly for use with a portable hand-held receiver for receiving analog and digital radio broadcast signals.